1. Field of the Invention
The present invention relates to a common line contact of a liquid crystal display (LCD) and a method of fabricating the same and, more specifically, to a common line contact of an LCD and a method of fabricating the same, in which the contact portion between a first common line formed during the fabrication of the gate of a thin film transistor (TFT), and second common line formed during the fabrication of the source and drain of the TFT is prevented from being disconnected, thereby improving the reliability of the device.
2. Discussion of Related Art
A liquid crystal display includes switching elements, such as thin film transistors (TFTs), and pixels having pixel electrodes transmitting or reflecting light, which are connected to the switching elements, and arranged in matrix. The LCD also includes a plurality of gate bus lines and data bus lines, which connect the pixels in a matrix to one another, and a plurality of pads formed at the end of the gate bus lines and data bus lines.
The LCD may also have storage capacitors in order to improve the characteristic of each pixel. The storage electrode of the storage capacitor should be maintained in common ground state by a ground signal externally applied. Accordingly, common lines are required to commonly transmit the ground signal externally applied to the storage electrode of the storage capacitor.
The common lines, which are formed during the fabrication of the TFT, include first common lines formed together with the gate bus lines and in parallel to them during the fabrication of the TFT's gate, and a second common line formed together with the data bus lines and in parallel to them during the fabrication of the TFT's source and drain. The first common lines are connected to the storage electrodes of the storage capacitors. The first common lines and second common line come into contact with each other at a contact portion, to transmit the ground signal of the second common line to the storage electrode through a plurality of first common electrodes.
FIG. 1 is a plan view of a common line contact portion of a conventional LCD. Referring to FIG. 1, first common lines 13 are formed around a TFT (not shown), together with the gate electrode (not shown) of the TFT. An anodized oxide layer 15 is formed on a predetermined portion of first common line 13. A gate bus line 14, which connects the gate electrode to an input pad (not shown), is formed between first common lines 13 during the fabrication of the gate electrode. Anodized oxide layer 15 is also formed on gate bus line 14. An exposed portion of first common lines 13 is connected to a data line (not shown), and electrically connected to a second common line 19 which is formed together with the TFT's source and drain (not shown).
FIG. 2 is a cross-sectional view taken along line I--I of FIG. 1. Referring to FIG. 2, the common line contact portion of the conventional LCD is constructed in such a manner that first common line 13 and gate bus line 14 are formed of an anodizable conductive metal on a transparent insulating substrate 11, the gate bus line being formed between first common lines 13. Anodized oxide layer 15 is formed on gate bus line 14 and on a predetermined portion of first common lines 13. An insulating layer 17 having a contact hole is formed of a silicon oxide (SiO.sub.2) or silicon nitride (Si.sub.3 N.sub.4) on first common lines 13. Second common line 19 is formed of a conductive metal on insulating layer 17 together with the source and drain, and electrically connected to first common lines 13. A passivation layer 21 is formed of an insulating material on second common line 19.
FIGS. 3A, 3B and 3C are cross-sectional views showing a conventional method of fabricating the common line contact of an LCD. Referring to FIG. 3A, an anodizable metal is deposited on transparent insulating substrate 11 through sputtering, and patterned by photolithography, forming first common lines 13. Here, gate bus line 14, which connects the gate electrode (not shown) to the input pad (not shown), is simultaneously formed between first common lines 13. The surface of gate bus line 14 and a predetermined portion of first common lines 13 is anodized, forming anodizing oxide layer 15.
Referring to FIG. 3B, a silicon oxide (SiO.sub.2) or silicon nitride (Si.sub.3 N.sub.4) is deposited on transparent substrate 11 and anodizing layer 15 including an exposed portion of first common lines 13 through chemical vapor deposition (CVD), forming insulating layer 17. A predetermined portion of insulating layer 17 is removed through photolithography, to expose first common lines 13.
Referring to FIG. 3C, a metal such as Cr is deposited on first common lines 13 and insulating layer 17 through CVD, to form second common line 19. An insulating material like silicon oxide (SiO.sub.2) or silicon nitride (Si.sub.3 N.sub.4) is deposited on second common line 19 through CVD, forming passivation layer 21.
The above-described conventional process of fabricating the common line contact of an LCD is simultaneously performed with the fabrication process of the TFT. Accordingly, indium tin oxide (ITO) (for forming the pixel electrode of the TFT) is also deposited on the passivation layer 21, so that the ITO deposited on the passivation layer is removed when the pixel electrode is patterned. Since the materials forming the first and second common lines have thermal expansion factors different from each other, cracking due to stress is generated at the portion where the first and second common lines come into contact with each other. When the ITO is removed, an etchant for etching the ITO permeates into the crack, etching the first and second common lines. Thus, the contact portion of the first and second common lines is disconnected, deteriorating the reliability of the device.